1. Technical Field
The invention relates to a semiconductor substrate equipped with a silicon carbide single crystal film that is expected as wide band gap semiconductor, and its manufacturing method.
2. Related Art
A silicon single crystal has a large diameter and high quality and can be manufactured at low cost, and therefore is used as a substrate for the growth of a single crystal of various materials. In particular, cubic silicon carbide (3C—SiC) is expected as a semiconductor material for low-loss power devices of the next generation, and is very advantageous as it can be grown in a single crystal (in heteroepitaxy) on an inexpensive silicon substrate.
However, there is a lattice constant difference of about 20% present between cubic silicon carbide crystal and silicon crystal, such that many voids and misfit dislocations are generated in the cubic silicon carbide crystal formed on the silicon crystal (silicon substrate), which makes it difficult to grow high quality crystals.
In this connection, Japanese Laid-open Patent Application 2004-103071 proposed a method for matching the lattice of the silicon substrate with the lattice of the cubic silicon carbide layer by inserting a cubic boron phosphide (c-BP) film between the silicon substrate and the cubic silicon carbide layer as a buffer layer for alleviating the lattice constant difference (lattice mismatch) between the silicon substrate and the cubic silicon carbide layer.
However, the melting point of c-BP is relatively low at about 1100° C., and the material including phosphorous would readily evaporate at temperatures lower than the melting point, such that it is very difficult to stably grow the buffer layer composed of c-BP on the silicon substrate. Cubic boron phosphide (c-BP) having a lattice constant of 0.4538 nm can make the lattice mismatch relatively smaller to 4.1% with respect to cubic silicon carbide (3C—SiC) having a lattice constant of 0.4358 nm, but a huge lattice mismatch of as much as 17.9% is still present between the silicon substrate (having a lattice constant of 0.5430 nm) and the cubic boron phosphide (c-BP). Therefore introduction of many defects into the c-BP film itself cannot be prevented, such that a high quality 3C—SiC single crystal film cannot be formed.
Under such circumstances, a buffer layer having a fewer lattice mismatch with respect to 3C—SiC is desired so that a sufficiently high quality single crystal film can be grown at the time of epitaxial growth of silicon carbide.